The present invention relates to a brake caliper for an automotive wheel brake system, and in particular, to a brake caliper with an improved brake force sensing.
Automotive wheel disk brakes rely upon the friction of opposing brake pads gripping a disk or rotor to slow a vehicle such as a car or truck. More particularly, a brake caliper supports opposing brake pads on opposite sides of the rotor. In operation, the caliper moves the pads together and squeezes the rotor therebetween. The rotor is connected to and rotates with a wheel of the vehicle. Thus, using the brake pads to squeeze the rotor slows the rotation of the rotor and vehicle wheel and hence, the speed of the vehicle itself. The resulting braking action depends on many factors, for example, the speed of the vehicle and hence, the angular velocity of the rotor, the condition of the rotor, the type and condition of the brake pads, ambient environmental conditions, for example, temperature, moisture, etc., and the magnitude of the force applied to the brake pads.
It is desirable to control braking forces in order to obtain optimal performance and reliability of the brake system. Excessive braking forces cause a build-up of heat that can damage the brake components and impair effective braking. In addition, excessive braking forces can cause a tire skid, especially when the tire is on a slippery road surface. However, in some circumstances, it is undesirable to reduce the braking forces, for example, where a shorter stopping distance is desired.
Conventional braking systems optimize braking forces in different braking situations, for example, to predict/prevent skidding, by monitoring indirect vehicle braking parameters, such as the rotational speed of the wheel and/or rotor. However, monitoring the wheel/rotor rotational speeds to detect a rapid slowing indicative of an impending tire skid avoids only one potential problem associated with excessive braking.
Another indirect vehicle braking parameter often monitored is the amount of hydraulic or electric power delivered to the brake caliper during a braking event. However, the pressure applied by the caliper against the brake pads to squeeze the rotor is only one factor affecting the resulting braking action. The braking system has many opportunities for the brake-actuating force to be diverted or reduced before a braking force is realized. More specifically, the braking action is a torque in a direction that is generally perpendicular to the caliper-generated, brake-actuating force applied to the brake pads. The braking torque produced by a particular brake-actuating force varies as a function of the coefficient of friction between the pads, that, in turn, is dependent on the aforementioned conditions. In addition, the available braking torque from a brake-actuating force is also impeded by internal friction of components of the brake caliper itself that diminish the effective brake-actuating force. Therefore, monitoring the power delivered to the brake caliper is not a particularly accurate measurement of the braking forces realized at the rotor. Rather, a measurement of the torque forces at the rotor and pads would be a better indicator of the effectiveness of a brake-generating force.
It is known to provide a system in which torsional stress produced by the brakes is indirectly sensed by a strain gauge placed in the axle of the vehicle rather than integral to the brake caliper. Such a system, however, has various drawbacks. Special considerations are required to specifically orient the sensor in the axle in order to measure torsional stress. Such an orientation requires a hole through the axle which is aligned at or about a brake caliper angle. This may be difficult to achieve. In addition, the axle is subject to a number of structural loads that complicate the signal conditioning from the strain gauge.
Therefore, a direct measurement of braking torque is desirable, but is not conventionally known or used in vehicle wheel braking systems.
The present invention provides an improved braking system. The braking system of the present invention is able to consistently and reliably determine the braking torque at the rotor disk. The braking system of the present invention is especially beneficial in providing a more precise control over how each wheel of a vehicle is braked; and thus, the braking system of the present invention provides improved vehicle control and stability under many adverse braking conditions.
According to the principles of the present invention and in accordance with the described embodiments, the invention provides an apparatus for use with a brake caliper having opposing brake pads positioned on opposite sides of a rotor. The brake caliper causes the brake pads to apply a braking force against the rotor that generates a braking torque. A torque transfer device is supported by the brake caliper and is in contact with one of the brake pads. The torque transfer device is movable with respect to the brake caliper in response to the braking torque, and a torque sensor is positioned in a sensing relationship relative to the torque transfer device. Thus, the torque sensor provides an output signal related to a change of position of the torque transfer device and the braking torque.
In one aspect of this invention, the torque transfer device is resiliently movable with respect to the brake caliper. In a further aspect of this invention, the torque sensor includes a magnet mounted on the torque transfer device and a magnet field sensor, for example, a Hall Effect sensor, is mounted on the brake caliper.
In another embodiment of the invention a method is provided for sensing a braking torque generated by a brake caliper forcing opposed brake pads against opposite sides of a rotor. The braking torque is opposed with a member in contact with a brake pad and movable relative to the brake caliper. A change in position of the member is sensed, and that change in position is related to a magnitude of the brake torque.
In one aspect of this invention, a change in a magnetic field caused by a change in position of the member is sensed by a magnetic field sensor, for example, a Hall Effect sensor. Further, an output signal is provided representing a change in the magnetic field and related to the braking torque.